Add additional unit tests for utils and EE (#3557)

## Summary
- add tests for LicenseKeyChecker
- expand GeneralUtils coverage
- cover extra PdfUtils functionality
- merge PdfUtilsMoreTest into PdfUtilsTest

## Testing
- `./gradlew test --no-daemon`
- `./gradlew build spotlessApply --no-daemon`

src/test/java/stirling/software/SPDF/utils/GeneralUtilsAdditionalTest.java

@@ -0,0 +1,41 @@
+package stirling.software.SPDF.utils;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import org.junit.jupiter.api.Test;
+
+class GeneralUtilsAdditionalTest {
+
+    @Test
+    void testConvertSizeToBytes() {
+        assertEquals(1024L, GeneralUtils.convertSizeToBytes("1KB"));
+        assertEquals(1024L * 1024, GeneralUtils.convertSizeToBytes("1MB"));
+        assertEquals(1024L * 1024 * 1024, GeneralUtils.convertSizeToBytes("1GB"));
+        assertEquals(100L * 1024 * 1024, GeneralUtils.convertSizeToBytes("100"));
+        assertNull(GeneralUtils.convertSizeToBytes("invalid"));
+        assertNull(GeneralUtils.convertSizeToBytes(null));
+    }
+
+    @Test
+    void testFormatBytes() {
+        assertEquals("512 B", GeneralUtils.formatBytes(512));
+        assertEquals("1.00 KB", GeneralUtils.formatBytes(1024));
+        assertEquals("1.00 MB", GeneralUtils.formatBytes(1024L * 1024));
+        assertEquals("1.00 GB", GeneralUtils.formatBytes(1024L * 1024 * 1024));
+    }
+
+    @Test
+    void testURLHelpersAndUUID() {
+        assertTrue(GeneralUtils.isValidURL("https://example.com"));
+        assertFalse(GeneralUtils.isValidURL("htp:/bad"));
+        assertFalse(GeneralUtils.isURLReachable("http://localhost"));
+        assertFalse(GeneralUtils.isURLReachable("ftp://example.com"));
+
+        assertTrue(GeneralUtils.isValidUUID("123e4567-e89b-12d3-a456-426614174000"));
+        assertFalse(GeneralUtils.isValidUUID("not-a-uuid"));
+
+        assertFalse(GeneralUtils.isVersionHigher(null, "1.0"));
+        assertTrue(GeneralUtils.isVersionHigher("2.0", "1.9"));
+        assertFalse(GeneralUtils.isVersionHigher("1.0", "1.0.1"));
+    }
+}